This invention relates to the dynamic scattering of nematic liquid crystalline compositions and particularly to such compositions comprising a pure trans-stilbene. More particularly, this invention relates to the surveilance and maintenance of conductance of nematic liquid crystalline compositions comprising a pure trans-stilbene in order to allow for the repetitive dynamic scattering of the composition.
Most nematic liquid crystalline materials are known to exhibit dynamic scattering. Dynamic scattering is generally observed in most nematic liquid crystalline materials upon application of an electrical field of sufficient strength to cause disruption of the alignment order of the nematic molecules and the resultant creation of relatively large regions of turbulence.
Without being under the influence of an aligning agent or an electrical field, the molecules of nematic liquid crystalline material point in one direction although the orientation differs from area to area.
Upon application of an electrical field across a layer of nematic liquid crystalline material, the molecules of the nematic line up with their long axes at some predetermined relationship to the field direction. When the electrical field is of sufficient strength to cause ions to move towards the electrodes by which the electrical field is applied, the ions disrupt the order of alignment of the nematic molecules and create relatively large regions of turbulence. Dynamic scattering of light results.
Dynamic scattering of pure trans-stilbene nematic liquid crystalline materials can not be achieved due to the large resistivities of the trans-stilbene materials.
It has been known that stilbenes exhibit "photosensitivity" in that in the presence of light these tended to decompose, and in the simultaneous presence of light and oxygen, phenantrene is formed. See, for example, U.S. Pat. No. 3,767,289.
In the liquid crystalline art, however, the high resistivity of nematic stilbenes have typically been modified, as in U.S. Pat. No. 3,767,289, by the addition of dopants. For example, ether complex salts have been used. I. Haller and G. Gladstone, Fourth International Liquid Crystal Conference, Kent, Ohio, Aug. 21-25, 1972.
U.S. Pat. No. 3,655,971 discloses exposure of liquid crystalline materials to ultra-violet radiation for imaging and without the application of voltage.
It has recently been discovered that nematic liquid crystalline compositions comprising a pure trans-stilbene can be made susceptible to dynamic scattering by irradiation with ultraviolet radiation. The electrical resistivity of the composition is thereby decreased and the conductance of the composition correspondingly increased. This technique is disclosed in copending U.S. applications Ser. No. 509,151, filed on Sept. 25, 1974 by Werner E. L. Haas and entitled "IMAGING METHOD."
In new and growing areas of technology such as liquid crystal imaging, new methods, apparatus, compositions, and articles of manufacture are often discovered for the application of the new technology in a new mode. The present invention relates particularly to a novel system for dynamically scattering pure trans-stilbene nematic liquid crystalline materials and more generally to maintaining a predetermined resistivity in mixtures of liquid crystalline materials including a trans-nematic stilbene.